Ft gtl apparatus and method for producing single synthetic crude oil

ABSTRACT

Disclosed are a Fischer-Tropsch (FT) gas-to-liquid (GTL) apparatus for producing unitary synthetic crude oil and an FT GTL method for producing unitary synthetic crude oil. The FT GTL apparatus for producing unitary synthetic crude oil of the present invention is an FT GTL apparatus for producing unitary synthetic crude oil from floating production, storage, and off-loading (FPSO), and characterized by comprising: a gas injection stabilization unit for performing stabilization on the produced natural gas to generate a natural gas condensate; and a modification unit for modifying the natural gas, which has been treated in the gas injection stabilization unit, to produce a synthetic crude oil product.

TECHNICAL FIELD

The present invention relates to an FT (Fischer-Tropsch) GTL (gas-to-liquid) apparatus and method for producing a single synthetic crude oil (syncrude) and, more particularly, to an FT GTL apparatus and method which can fluidize FT wax, which is an intermediate synthetic crude oil product (FT naphtha, FT heavy oil, FT wax) produced by chemical processes in a GTL floating production, storage, and off-loading (FPSO) and is in a solid state causing difficulty in transportation, by subjecting some of the FT wax to a low level of general hydrocracking or mild hydroisomerization and mixing FT naphtha and FT heavy oil with the FT wax such that the resulting product can be stored and transported in a solid state.

BACKGROUND ART

Recently, as petroleum resources are on the brink of being exhausted, there is demand for alternative resources capable of producing transportation oils, fuel oils, and petrochemicals. Representative examples of hydrocarbon materials that can meet such demand include coal and natural gas, deposits of which are abundant, and alternative eco-friendly hydrocarbon sources such as biomass or wastes can be used in order to achieve CO₂ reduction for prevention of global warming. As a method of producing chemicals such as transportation oils including gasoline and diesel, alcohols, wax, lube base oils, or olefins from such alternative hydrocarbon sources, an indirect coal liquefaction (coal-to-liquid (CTL)) process, a process of producing synthetic distillates from natural gas (gas-to-liquid (GTL) process), and an indirect biomass liquefaction (biomass-to-liquid (BTL)) process are well known in the art.

An FT GTL process includes converting syngas, in which a small amount of methane and carbon dioxide are contained and hydrogen is mixed with carbon monoxide, into large hydrocarbon molecules using a high pressure catalyst reactor. In other words, an FT synthesis reaction in a reactor for Fischer-Tropsch synthesis is as follows:

CO+2H₂→-CH₂+H₂O ΔH(227° C.)=−165 kJ/mol

Methanation reaction

CO+3H₂→CH₄+H₂O ΔH(227° C.)=−215 kJ/mol

water gas shift

CO+H₂O

CO₂+H₂ΔH(227° C.)=−40 kJ/mol

Boudouard reaction

2CO

C+CO₂ΔH(227° C.)=−134 kJ/mol

Here, as a catalyst, an iron oxide-based catalyst or a cobalt-based catalyst is used; the reaction temperature ranges from 200° C. to 350° C.; and the reaction pressure ranges from 10 bar to 30 bar. Such an FT synthesis reaction is a moderate exothermic reaction, and thermal control through heat exchange, which is a key determinant in design of the reactor, is important in order to increase the catalytic reaction rate.

An FT product produced by the catalyst reactor is composed of unreacted syngas, methane, ethane, LPG (C3 to C4), naphtha (C5 to C10), heavy oil (C11 to C22), and wax (>C22). Essentially, several hundreds of components having carbon numbers of 1 to 40 or more are produced through FT synthesis.

Relative amount of each of the above components in an untreated product mainly depends on the reaction temperature of the reactor and the kind of catalyst used. Generally, there are three types of basic FT operating systems, that is, high temperature FT reaction using an iron-based catalyst (HTFT-Fe), low temperature FT reaction using an iron-based catalyst (LTFT-Fe), and low temperature FT reaction using a cobalt-based catalyst (LTFT-Co).

An FPSO unit is a floating vessel for production, storage, and offloading of crude oil and serves to produce and store crude oil and to offload the crude oil onto a crude oil transportation means such as an oil tanker at sea.

The FPSO unit includes drilling facilities for off-shore drilling and an oil/gas separator for separating glassy oil into crude oil and associated gas. In addition, the FPSO unit includes storage facilities for storing crude oil and an offloading means capable of transferring crude oil to a crude oil transportation means.

Generally, associated gas incidentally generated in the FPSO process is burned and discharged to air or is compressed and reintroduced into an undersea disused oil well. Thus, FPSO-GTL and FPSO-DME processes using such an associated gas as a raw material for the GTL process after on-board preparation of syngas are commonly employed. Further, natural gas extracted directly from a marginal gas field may be used in an FPSO-GTL process of producing a synfuel or in an FPSO-LNG process for direct liquefaction.

Examples of such technology are disclosed in Patent Documents 1 and 2.

For example, Patent Document 1 discloses an off-shore FPSO-DME apparatus for direct synthesis of DME which includes FPSO equipment including a glassy oil separator and an oil/gas separation unit, a reforming reactor, a dimethyl ether reactor, an undersea CO₂ storage device, and a power system for internal power generation, wherein a hydrogen separator and a carbon dioxide separation unit are disposed between the reforming reactor and the dimethyl ether reactor and the carbon dioxide separation unit is connected to the dimethyl ether reactor such that carbon dioxide from the carbon dioxide separation unit, and water and carbon dioxide generated in the power system for internal power generation are recycled to the reforming reactor and surplus carbon dioxide is stored undersea.

Patent Document 2 discloses an off-shore FPSO-GTL apparatus which includes: FPSO equipment including a glassy oil separator separating glassy oil extracted from an oil field into an associated gas and crude oil and an oil/gas separation unit separating the separated crude oil into oil and gas; a reforming reactor receiving a gas obtained by removing an H₂S component from a C₁ to C₄ carbon compound using a desulfurizer, wherein the carbon compound is separated from the gas supplied from the FPSO equipment; a liquid-phase carbon compound preparation device preparing a liquid-phase carbon compound using syngas passing through the reforming reactor; an upgrading reactor receiving hydrogen obtained by subjecting syngas passing through the reforming reactor to a water gas shift reaction; an undersea CO₂ storage device receiving surplus carbon dioxide obtained by removing hydrogen from the syngas; and a power system for internal power generation of the FPSO-GTL apparatus, wherein a hydrogen separator and a carbon dioxide separation unit are disposed between the reforming reactor and the liquid-phase carbon compound preparation apparatus, and a water separator is disposed between the liquid-phase carbon compound preparation apparatus and the upgrading reactor, such that water and carbon dioxide from the water separator and the carbon dioxide separation unit and water and carbon dioxide generated in the power system for internal power generation are recycled to the reforming reactor and surplus carbon dioxide is stored undersea.

Synthetic crude oil is a fuel artificially prepared using resources other than petroleum, such as natural gas, coal, or biomass and is developed as next generation clean fuel technology by major companies and institutions under the government administration in Korea. Since demand for a GTL clean fuel is expected to rapidly increase in the future given increasing oil prices, such synthetic crude oil technology is considered to be economically feasible.

In this context, although development of a GTL FPSO aimed at allowing technology on land to be realized at sea is proceeding, there are many problems to solve before commercialization. One of such problems involved with the GTL FPSO is an issue of securing flowability for storage and transportation of GTL synthetic crude oil. This is due to the fact that a synthetic crude oil produced in the GTL FPSO contains a large amount of wax and thus exhibits high viscosity. Thus, flowability of the synthetic crude oil is crucial to secure efficient operation and economic feasibility of the GTL FPSO.

For this purpose, there has been proposed a method in which a synthetic crude oil is heated to a temperature at which the synthetic crude oil can exhibit flowability based on a concept as in a typical very large crude oil carrier (VLCC). However, this method requires additional facilities and fuel supply to continuously maintain the temperature during a series of processes including production/storage/offloading/separation.

As one example of the related art, Korean Patent No. 0,339,993 discloses a fluidization method which includes bringing tar/sludge into contact with an effective amount of a surfactant and an effective amount of an inorganic acid and/or a carrier, wherein the inorganic acid is sulfuric acid, phosphoric acid or a mixture thereof and is introduced from a container/tube to wash or fluidize tar/sludge. Thus, this method is expected to remove tar/sludge such that the resulting product can be easily transported, handled, and pumped.

However, this method is aimed at washing tar/sludge without causing physical deformation of a pipe and a storage tank, and is thus difficult to use to secure flowability so as to facilitate transportation and use of a synthetic crude oil produced in the GTL FPSO.

DISCLOSURE Technical Problem

A conventional technique as described above has a problem in that a refinery apparatus for completely shifting LPG, gasoline, kerosene, diesel, or the like into a light material through hydrocracking of wax includes a product fractionating apparatus as well as a large expensive hydrocracking apparatus, thereby causing increase in production costs.

In addition, the conventional technique has a problem in that three types of products produced by a refinery process are individually stored and transported, thereby causing increase in transportation costs.

The present invention has been conceived to solve such problems in the art and it is an aspect of the present invention to provide an FT GTL apparatus and method for producing a single synthetic crude oil (syncrude) which can produce a single synthetic crude oil using as few devices as possible.

It is another aspect of the present invention to provide an FT GTL apparatus and method for producing a single synthetic crude oil which can reduce complexity and costs involved with storage of FPSO products and transportation of the products to an on-shore refinery.

It is a further aspect of the present invention to provide an apparatus for adjusting wax content in a GTL FPSO synthetic crude oil which allows production and mixing to be achieved with wax content in a synthetic crude oil produced in a GTL FPSO adjusted to a predetermined level to secure flowability of the synthetic crude oil, thereby improving economic feasibility of a series of processes including production, storage, offloading, transportation, and separation of the synthetic crude oil.

Technical Solution

In accordance with one aspect of the present invention, a Fischer-Tropsch (FT) gas-to-liquid (GTL) apparatus for producing a single synthetic crude oil in a floating production, storage, and off-loading (FPSO) unit includes:

a gas injection stabilization unit producing a natural gas condensate by stabilizing produced natural gas; and

a reforming unit producing a synthetic crude oil product by reforming the natural gas treated in the gas injection stabilization unit.

Preferably, the FT GTL apparatus further includes a product treatment unit mixing the natural gas condensate with the synthetic crude oil product to produce a single synthetic crude oil.

Preferably, the gas injection stabilization unit includes a first three-phase separator separating CH₁ to CH₄₀ and H₂O injected in the separator into CH₁ to CH₄, the natural gas condensate (CH₅ to CH₄₀), and water (H₂O).

Preferably, the synthetic crude oil product is FT naphtha, FT heavy oil, and FT wax, and the reforming unit includes an FT reactor producing the FT wax and a second three-phase separator producing a first mixture of the FT naphtha and the FT heavy oil.

Preferably, the second three-phase separator separates syngas treated in the FT reactor into a tail gas, H₂O, and the first mixture through heat exchange of the syngas in a first heat exchanger.

Preferably, the product treatment unit includes: a product mixing tank mixing the first mixture with a second mixture of the FT naphtha, the FT heavy oil, and the FT wax and the natural gas condensate; and a storage tank storing a GTL liquid prepared in the product mixing tank.

Preferably, the product treatment unit further includes a second heat exchanger performing heat exchange of the FT wax produced in the FT reactor, a reactor producing the second mixture by subjecting the FT wax heat exchanged in the second heat exchanger to hydrocracking or mild hydroisomerization, and a separator separating unreacted tail gas from the second mixture.

Preferably, the product treatment unit further includes a first compressor for compressing a tail gas and a second compressor performing hydrogenation, and the unreacted tail gas separated in the separator is supplied to the second heat exchanger through the first compressor and the second compressor.

Preferably, the FT GTL apparatus further includes a tail gas separation unit separating the synthetic crude oil into a tail gas and a first mixture of FT naphtha and FT heavy oil, and

the first mixture separated in the tail gas separation unit is supplied to the product treatment unit.

Preferably, the reforming unit includes: an F-T synthesis unit producing synthetic oil from syngas produced from the natural gas; and a control unit controlling the F-T synthesis unit to maintain wax content in the synthetic crude oil reformed into the synthetic oil at a predetermined level so as to adjust wax content of the synthetic crude oil.

Preferably, the F-T synthesis unit is provided with an LT-FT reactor and an HT-FT reactor in series or in parallel and adjusts flow rates of the LT-FT reactor and the HT-FT reactor depending upon the composition of synthetic crude oil produced at a downstream side of the F-T synthesis unit.

Preferably, the control unit is provided with a wax detection unit detecting wax content in the synthetic crude oil and an unreacted gas detection unit detecting unreacted gas content.

Preferably, the control unit controls the wax content to be maintained at a minimum level to a degree to which unreacted gas content is maintained within a predetermined range.

In accordance with another aspect of the present invention, a Fischer-Tropsch (FT) gas-to-liquid (GTL) method for producing a single synthetic crude oil in a floating production, storage, and off-loading (FPSO) unit includes:

(a) producing a natural gas condensate from natural gas;

(b) producing FT wax and a first mixture of FT naphtha and FT heavy oil from syngas;

(c) producing a second mixture of FT naphtha, FT heavy oil, and FT wax; and

(d) producing a single synthetic crude oil by mixing the natural gas condensate with the first mixture and the second mixture.

Preferably, step (c) is performed though hydrocracking or mild hydroisomerization of wax.

Preferably, the single synthetic crude oil produced in step (d) is stored and transported without heat treatment.

Preferably, the FT GTL method further includes: (e) refining the single synthetic crude oil in an on-shore refinery plant.

Advantageous Effects

According to the present invention, it is possible to provide an FT GTL apparatus and method for producing a single synthetic crude oil which can save deck space in an FPSO while reducing production costs due to use of simple product upgrading equipment, and allows the FPSO to only require one tank to store products and eliminates a need for additional heat supply needed to store the products and transfer the products to a pump, thereby reducing transportation costs.

In addition, according to the present invention, it is possible to provide an FT GTL apparatus and method for producing a single synthetic crude oil which subjects some of FT wax to a low level of general hydrocracking or mild hydroisomerization after mixing FT naphtha with FT heavy oil so as to allow a synthetic crude oil to be transported without being heated, thereby reducing complexity, space, and cost as compared with the case of using a refinery apparatus provided with a high pressure hydrocracking reaction unit while reducing hydrogen consumption as compared with the case of using such a refinery apparatus.

Further, according to the present invention, it is possible to secure flowability of a synthetic crude oil produced in a GTL FPSO, thereby improving economic feasibility of a series of processes including production, storage, offloading, transportation, and separation of the synthetic crude oil, such that marketable technology can be accumulated in the related art.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an FT GTL apparatus for producing a single synthetic crude oil according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating connection between the main units of FIG. 1.

FIG. 3 is a flowchart illustrating an FT GTL method of producing a single synthetic crude oil according to the first embodiment of the invention

FIG. 5 is a view illustrating production, storage, offloading, transportation, and separation of a single synthetic crude oil according to the first embodiment of the invention.

FIG. 6 is a flowchart showing main processes of a GTL FPSO according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing main parts of an F-T synthesis unit of FIG. 6.

FIG. 8 is a synthetic crude oil weight fraction diagram illustrating control according to the second embodiment of the invention.

EMBODIMENTS

The above and other aspects, features, and advantages of the present invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings.

First, the concept of the present invention will be described.

A GTL FPSO is an off-shore structure in which a GTL unit is incorporated into an FPSO (Floating Production, Storage, and Off-loading) unit so as to produce clean energy at sea. A GTL process is composed of a reforming process of producing syngas (H₂, CO) from natural gas (NG), a Fischer-Tropsch (F-T) process of producing synthetic crude oil from the syngas, and an upgrading process of converting the synthetic crude oil into a fuel having a desired carbon number.

In the GTL FPSO, securing flowability and transferability of a synthetic crude oil is an issue of growing importance for commercialization. For this purpose, although installation of upgrading equipment is considered, there is high probability of performance and safety problems given the fact that such equipment has not yet been installed at sea.

First, in a first embodiment of the present invention, a single synthetic crude oil product transferable from the FT GTL FPSO can be produced. In other words, the first embodiment of the invention provides a novel concept of producing single hybrid FT synthetic crude oil which is a mixture of FT naphtha, FT heavy oil and treated FT wax, and can be stored and transferred without heat treatment.

The concept of single hybrid FT synthetic crude oil requires a catalyst, reactor design, and operating system suitable for wax hydrocracking or mild hydroisomerization. In addition, such a concept of the single hybrid FT synthetic crude oil can reduce space and costs for processing FT products while simplifying storage and transportation requirements for FT GTL FPSO products.

Further, synthetic crude oil produced in each of plural FT GTL FPSOs is transferred to a single on-shore refinery plant and is treated therein. In addition, the synthetic crude oil may be produced into a marketable fuel for vehicles through mixing with general crude oil products and/or through additional refinement. Such a concept is useful because the concept can operate a carrier fleet more efficiently and minimize spatial, capital requirements for the FPSO while allowing a system that can benefit from economies of scale in an on-shore refinery plant.

According to the first embodiment of the invention, after FT naphtha is mixed with FT heavy oil, some of FT wax is subjected to a low level of general hydrocracking or mild hydroisomerization such that the synthetic crude oil can be transported without heat treatment. Such a concept includes transforming mixed synthetic crude oil such that the synthetic crude oil can be stored and transported without heat treatment, although the concept includes using a catalyst and operating system not intended to produce a final FT product. In addition, this concept also includes using different catalysts to produce different products without diluting (or mixing) FT naphtha and FT heavy oil with treated FT wax.

The above concept includes subjecting FT wax to hydrocracking or mild hydroisomerization in order to only increase the pour point and freezing point of the synthetic crude oil without trying to modify other properties. Thus, it is possible to reduce costs required for processing an FPSO on-board FT product while providing size and space reduction and simplifying storage and transportation of the product.

Hereinafter, the first embodiment of the invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of an FT GTL apparatus for producing a single synthetic crude oil according to the first embodiment of the invention.

Referring to FIG. 1, the FT GTL apparatus for producing a single synthetic crude oil according to the first embodiment is an FT GTL apparatus for producing a single synthetic crude oil in an FPSO, and includes a gas injection stabilization unit 10 receiving produced gas, a desulfurization unit 20, a natural gas saturation and pre-reforming unit 30, a small reforming unit 40, a syngas conditioning unit 50, an FT synthesis unit 60, a tail gas separation unit 70, and a product treatment unit 80.

The gas injection stabilization unit 10 performs stabilization of produced raw natural gas (NG) to produce natural gas, a natural gas condensate (NG condensate), and water (H₂O), wherein the natural gas condensate is supplied to the product treatment unit 80.

The desulfurization unit 20 removes sulfur from the natural gas and supplies the raw natural gas to the natural gas saturation and pre-reforming unit 30. Some of the raw natural gas having been pre-treated in the natural gas saturation and pre-reforming unit 30 is used as a fuel gas, and the rest of the natural gas is heated by steam and then supplied to the reforming unit 40 and discharged to a saturator.

The reforming unit 40 reforms the steamed natural gas supplied from the natural gas saturation and pre-reforming unit 30 into raw syngas, thereby producing a synthetic crude oil product. In addition, a gas untreated in the reforming unit 40 is supplied to the natural gas saturation and pre-reforming unit 30 as a fuel gas.

The raw syngas treated in the reforming unit 40 is produced into syngas in the syngas conditioning unit 50, and H₂ generated in this process is supplied to the reforming unit 40 and the product treatment unit 80 as a fuel gas. Further, the syngas condensate generated in the syngas conditioning unit 50 is supplied to the natural gas saturation and pre-reforming unit 30 or discharged.

The syngas supplied from the syngas conditioning unit 50 is passed through the FT synthesis unit 60 to be separated into FT wax and a first mixture of FT naphtha and FT heavy oil, which, in turn, are supplied to the product treatment unit 80.

The tail gas separation unit 70 separates the syngas supplied from the FT synthesis unit 60 into a tail gas and the first mixture of FT naphtha and FT heavy oil, wherein the first mixture is supplied to the product treatment unit 80, and the tail gas is discharged in part or recycled to the natural gas saturation and pre-reforming unit 30.

The product treatment unit 80 serves to mix the natural gas condensate supplied from the gas injection stabilization unit 10 with the first mixture and the FT wax supplied from the FT synthesis unit 60 and the first mixture supplied from the tail gas separation unit 70 to produce a single synthetic crude oil according to the present invention.

Boiler feed water (BFW) for steam formation is supplied to the reforming unit 40 and the syngas conditioning unit 50.

Next, configurations of the gas injection stabilization unit 10, the reforming unit 40, and the product treatment unit 80, which are main features of the first embodiment of the invention, will be described with reference to FIG. 2.

FIG. 2 is a block diagram illustrating connection between the main units of FIG. 1.

Referring to FIG. 2, the gas injection stabilization unit 10 includes a first three-phase separator 41 which separates received CH₁ to CH₄₀ and H₂O into CH₁ to CH₄, the natural gas condensate (CH₅ to CH₄₀) and water (H₂O). The natural gas condensate (CH₅ to CH₄₀) is supplied to the product treatment unit 80, and the water (H₂O) is supplied to the natural gas saturation and pre-reforming unit 30.

The reforming unit 40 includes an FT reactor 41 producing FT wax from the natural gas and a second three-phase separator 42 producing the first mixture of FT naphtha and FT heavy oil. The second three-phase separator 42 separates the syngas treated in the FT reactor 41 into a tail gas, H₂O, and the first mixture through heat exchange in a first heat exchanger 43. The first mixture is supplied to the product treatment unit 80.

The product treatment unit 80 includes: a product mixing tank 81 for mixing the first mixture supplied from the second three-phase separator 42 with the natural gas condensate supplied from the gas injection stabilization unit 10 and a second mixture of FT naphtha, FT heavy oil, and FT wax; a storage tank 82 storing a GTL liquid prepared in the product mixing tank 81; a second heat exchanger 83 performing heat exchange of the FT wax produced in the FT reactor 41; a reactor 84 producing the second mixture through hydrocracking or mild hydroisomerization of the FT wax subjected to heat exchange in the second heat exchanger 83; and a separator 85 for separating unreacted tail gas from the second mixture.

The single synthetic crude oil product according to the present invention is prepared by mixing FT wax with FT naphtha and FT heavy oil. As described above, the single synthetic crude oil product is obtained by mixing the first mixture of FT naphtha and FT heavy oil with the second mixture of FT naphtha, FT heavy oil, and FT wax, and the natural gas condensate in the product mixing tank 81, followed by storage in the storage tank 82.

The single synthetic crude oil product prepared as above allows the FPSO to need only one tank to store the product, i.e. the storage tank 82 and can eliminate a need for additional heat supply for storage of the product and transfer of the product to a pump, thereby reducing transportation costs.

In addition, the product treatment unit 80 further includes a first compressor 86 which compresses the tail gas separated in the separator 85 and a second compressor 87 which performs hydrogenation, wherein unreacted tail gas separated in the separator 85 is supplied to the second heat exchanger 83 through the first compressor 86 and the second compressor 87.

Next, a process of performing production, storage, offloading, transportation, and separation of the single synthetic crude oil using the FT GTL apparatus for producing a single synthetic crude oil as shown in FIGS. 1 and 2 will be described with reference to FIGS. 3 and 4.

FIG. 3 is a flowchart illustrating an FT GTL method of producing a single synthetic crude oil according to the first embodiment of the invention, and FIG. 4 is a view illustrating production/storage/offloading/transportation/separation of a single synthetic crude oil according to the first embodiment of the invention.

The FT GTL method of producing a single synthetic crude oil according to the first embodiment of the invention is an FT GTL method for producing a single synthetic crude oil in an FPSO, and, in the method, first, natural gas is subjected to stabilization in the gas injection stabilization unit 10 to produce a natural gas condensate (S10).

Thereafter, sulfur is removed from the natural gas by the desulfurization unit 20, and a syngas is produced by the natural gas saturation and pre-reforming unit 30 and the small reforming unit 40.

In the reforming unit 40, FT wax and the first mixture of FT naphtha and FT heavy oil are produced from the syngas (S20).

Then, in the product treatment unit 80, the FT wax is subjected to hydrocracking or mild hydroisomerization to produce the second mixture of FT naphtha, FT heavy oil, and FT wax (S30).

In addition, in the product treatment unit 80, the natural gas condensate produced in step S10 is mixed with the first mixture produced in step S20 and the second mixture produced in step S30 to produce a single synthetic crude oil (S40).

As shown in FIG. 4, the single synthetic crude oil produced in step S40 is stored and transported without heat treatment (S50). The single synthetic crude oil transported in step S50 is refined in an on-shore refinery plant (S60).

According to the second embodiment of the invention, the FT synthesis unit 600 is provided to produce synthetic oil from syngas prepared from natural gas. Referring to FIG. 5, a GTL main process is performed by the natural gas saturation and pre-reforming unit 300, the reforming unit 400, the syngas conditioning unit 500, the FT synthesis unit 600, and the product treatment unit 800, which are sequentially connected to one another. The FT synthesis unit 600 serves to convert the syngas into the synthetic oil, and the product treatment unit 800 serves to upgrade the synthetic oil to produce a synthetic crude oil. A surplus syngas generated in the FT synthesis unit 600 is fractionated in the tail gas separation unit 700 to be partially recycled to the pre-reforming unit 20. The synthetic crude oil produced in the product treatment unit 800 is stored in a tank.

Here, since the synthetic crude oil produced in the GTL FPSO exhibits high viscosity due to containing a large amount of wax, it is necessary to secure flowability of the synthetic crude oil so as to facilitate storage, offloading, and transportation. As the amount of the wax approaches 100%, the synthetic crude oil is more likely to be solidified at atmospheric pressure/room temperature, such that storage and offloading of the synthetic crude oil is impossible.

According to the second embodiment, a control unit 900 controls the FT synthesis unit 600 to maintain wax content in the synthetic crude oil that will be reformed into the synthetic oil at a predetermined level. The control unit 900 determines the state of the synthetic crude oil stored in the tank and executes an algorithm for maintaining the wax content at an optimal level based on the determination.

According to details of the second embodiment, the FT synthesis unit 600 is provided with an LT-FT reactor 620 and an HT-FT reactor 640 in series or in parallel and adjusts a flow rate of the LT-FT reactor 620 and the HT-FT reactor 640 depending upon the composition of a synthetic crude oil produced at a downstream side thereof. Referring to FIG. 2, the FT synthesis unit 600 includes the HT-FT reactor 640 at a downstream side of the LT-FT reactor 620. The LT-FT reactor 620 is operated at a temperature of 220° C. to 250° C. and mainly produces a liquid product such as a heavy oil fraction or wax, and the HT-FT reactor 640 is operated at a temperature of 330° C. to 350° C. and produces a gaseous product such as gasoline or naphtha.

When the LT-FT reactor 620 and the HT-FT reactor 640 are operated at the same time, it is possible to easily secure flowability of the synthetic crude oil through adjustment of the amount of the wax. In FIG. 6, reference numeral 48 denotes a separator for removing moisture and the like after the synthetic reaction.

Referring to FIG. 7, it is shown from marks at the right side that the wax is present in an amount of about 50% after primary reaction in the LT-FT reactor 620, and it is shown from marks at the left side that the amount of the wax is reduced to about 10% and the amount of naphtha is increased after the secondary reaction in the HT-FT reactor 640.

The LT-FT reactor 620 may be disposed at a downstream side of the HT-FT reactor 640 depending upon desired properties of the synthetic crude oil. Examples of the above case may include the case of trying to produce a light synthetic crude oil such as gasoline, naphtha, or diesel in large amounts.

According to details of the second embodiment, the control unit 900 is provided with a wax detection unit 920 detecting wax content, an unreacted gas detection unit 940 detecting unreacted gas content, and a driving unit 960. The wax detection unit 920 and the unreacted gas detection unit 940 are not limited to hardware such as a specific sensor and may include a database in which data of changes in content for each component of the synthetic crude oil are collected and software.

According to details of the second embodiment, the control unit 900 maintains wax content at a minimum level to a degree to which unreacted gas content is maintained within a predetermined range. As shown in FIG. 3, as wax content of the synthetic crude oil is decreased, transport efficiency is reduced due to increasing content of unreacted gas such as LPG. Thus, the control unit maintains wax content at an optimal level to a degree to which content of unreacted gas is maintained within a predetermined range. It should be understood that wax content must also be maintained within a range capable of securing flowability of the synthetic crude oil.

As such, both the LT-FT reactor 620 and the HT-FT reactor 640 are used commercially in on-shore facilities and thus have low risk when applied to off-shore facilities. Thus, it is not necessary to secure flowability through an upgrading process, which is unproven in off-shore facilities, and it is possible to reduce CAPEX and OPEX required for establishment of an upgrading system.

Although some embodiments have been described, it will be apparent to those skilled in the art that these embodiments are given by way of illustration only, and that various modifications, changes, alterations, and equivalent embodiments can be made without departing from the spirit and scope of the invention. The scope of the invention should be limited only by the accompanying claims and equivalents thereof. 

1. A Fischer-Tropsch (FT) gas-to-liquid (GTL) apparatus for producing a single synthetic crude oil in a floating production, storage, and off-loading (FPSO) unit, comprising: a gas injection stabilization unit producing a natural gas condensate by stabilizing produced natural gas; and a reforming unit producing a synthetic crude oil product by reforming the natural gas treated in the gas injection stabilization unit.
 2. The FT GTL apparatus according to claim 1, further comprising: a product treatment unit mixing the natural gas condensate with the synthetic crude oil product to produce a single synthetic crude oil.
 3. The FT GTL apparatus according to claim 2, wherein the gas injection stabilization unit comprises a first three-phase separator separating CH₁ to CH₄₀ and H2O injected in the separator into CH₁ to CH₄, the natural gas condensate (CH₅ to CH₄₀), and water (H2O).
 4. The FT GTL apparatus according to claim 3, wherein the synthetic crude oil product is FT naphtha, FT heavy oil, and FT wax, and the reforming unit comprises an FT reactor producing the FT wax and a second three-phase separator producing a first mixture of the FT naphtha and the FT heavy oil.
 5. The FT GTL apparatus according to claim 4, wherein the second three-phase separator separates syngas treated in the FT reactor into a tail gas, H₂O, and the first mixture through heat exchange of the syngas in a first heat exchanger.
 6. The FT GTL apparatus according to claim 5, wherein the product treatment unit comprises: a product mixing tank mixing the first mixture with a second mixture of the FT naphtha, the FT heavy oil, and the FT wax and the natural gas condensate; and a storage tank storing a GTL liquid prepared in the product mixing tank.
 7. The FT GTL apparatus according to claim 6, wherein the product treatment unit further comprises a second heat exchanger performing heat exchange of the FT wax produced in the FT reactor, a reactor producing the second mixture by subjecting the FT wax subjected to heat exchange in the second heat exchanger to hydrocracking or mild hydroisomerization, and a separator separating unreacted tail gas from the second mixture.
 8. The FT GTL apparatus according to claim 7, wherein the product treatment unit further comprises a first compressor for compressing a tail gas and a second compressor for adding hydrogen, and the unreacted tail gas separated in the separator is supplied to the second heat exchanger through the first compressor and the second compressor.
 9. The FT GTL apparatus according to claim 2, further comprising: a tail gas separation unit separating the synthetic crude oil into a tail gas and a first mixture of FT naphtha and FT heavy oil, and the first mixture separated in the tail gas separation unit is supplied to the product treatment unit.
 10. The FT GTL apparatus according to claim 1, wherein the reforming unit comprises: an F-T synthesis unit producing synthetic oil from syngas produced from the natural gas; and a control unit controlling the F-T synthesis unit to maintain wax content in the synthetic crude oil reformed into the synthetic oil at a predetermined level so as to adjust wax content of the synthetic crude oil.
 11. The FT GTL apparatus according to claim 10, wherein the F-T synthesis unit is provided with an LT-FT reactor and an HT-FT reactor in series or in parallel and adjusts flow rates of the LT-FT reactor and the HT-FT reactor depending upon the composition of a synthetic crude oil produced at a downstream side of the F-T synthesis unit.
 12. The FT GTL apparatus according to claim 10, wherein the control unit is provided with a wax detection unit detecting wax content of the synthetic crude oil and an unreacted gas detection unit detecting unreacted gas content.
 13. The FT GTL apparatus according to claim 12, wherein the control unit controls the wax content to be maintained at a minimum level to a degree to which unreacted gas content is maintained within a predetermined range.
 14. A Fischer-Tropsch (FT) gas-to-liquid (GTL) method for producing a single synthetic crude oil in a floating production, storage, and off-loading (FPSO) unit, comprising: (a) producing a natural gas condensate from natural gas; (b) producing FT wax and a first mixture of FT naphtha and FT heavy oil from syngas; (c) producing a second mixture of FT naphtha, FT heavy oil, and FT wax; and (d) producing a single synthetic crude oil by mixing the natural gas condensate with the first mixture and the second mixture.
 15. The FT GTL method according to claim 14, wherein step (c) is performed though wax hydrocracking or mild hydroisomerization.
 16. The FT GTL method according to claim 15, wherein the single synthetic crude oil produced in step (d) is stored and transported without heat treatment.
 17. The FT GTL method according to claim 15, further comprising: (e) refining the single synthetic crude oil in an on-shore refinery plant. 